CN113687099A - PIV image calibration device and method based on laser linear array - Google Patents
PIV image calibration device and method based on laser linear array Download PDFInfo
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- G—PHYSICS
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/18—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance
- G01P5/20—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance using particles entrained by a fluid stream
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- G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
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- G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
- G01M9/08—Aerodynamic models
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- G—PHYSICS
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups
- G01P21/02—Testing or calibrating of apparatus or devices covered by the preceding groups of speedometers
- G01P21/025—Testing or calibrating of apparatus or devices covered by the preceding groups of speedometers for measuring speed of fluids; for measuring speed of bodies relative to fluids
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Abstract
The invention discloses a PIV image calibration device and method based on a laser linear array, relates to the technical field of laser speed measurement and image restoration, and can solve the problem of image distortion caused by model shock waves in a high-tide wind tunnel and realize distortion capture and correction. The device includes: the laser emitting component is used for emitting laser linear arrays with equal spacing characteristics; the optical assembly is used for carrying out light splitting treatment on the laser line so as to form a laser grating in an experimental observation area; the camera is used for acquiring a distorted laser grating image when the working condition of the wind tunnel experimental section model is adjusted to a PIV experimental working condition; and the background processor is used for calibrating and repairing the distorted laser grating image based on a distortion recovery calibration algorithm of the neural network. The method can accurately acquire the shock wave distortion image in the real model experiment, and further acquire the spatial resolution of the image at each position.
Description
Technical Field
The invention relates to the technical field of laser speed measurement and image restoration, in particular to a PIV image calibration device and method based on a laser linear array.
Background
The Particle Image Velocimetry (PIV) technology is a non-contact flow velocity field optical measurement technology, and the technology realizes the measurement of the movement velocity in a flow velocity field represented by Particle micelles by tracking the cross-frame displacement of the Particle micelles on two frames of Particle images captured by a laser camera system, and is widely applied to wind tunnel experiments.
Before recording the particle track image, the image spatial resolution needs to be calibrated. According to the conventional method, targets of the black and white chess pieces are placed in a detected area, and after the targets are collected by a camera, a distorted mathematical model is solved by using recorded angular point coordinates, and the image space resolution of each position is obtained. However, there are certain problems in high-tide wind tunnels, specifically: because the wind speed is higher, so can produce the shock wave in local when placing the target in the region of being surveyed, the shock wave can make the local optical diffraction phenomenon that produces of region of being surveyed to make the particle track image of record produce the distortion, the distortion effect that just produces comparatively complicacy here, and then can't accurately obtain everywhere image space resolution.
The target is placed in a detected area, and if the target is in a static windless condition, shock waves cannot be obtained, distortion cannot be generated, and further image space resolution at each position cannot be obtained; if under windy conditions, the target can cause shock waves again, a more complex distortion effect can be generated, and the spatial resolution of images at all positions cannot be accurately obtained. Obviously, the above methods cannot obtain a shock wave distortion image in a real model experiment, and further cannot obtain image spatial resolution at various positions.
Disclosure of Invention
The invention aims to provide a PIV image calibration device and method based on a laser linear array so as to achieve the purpose of accurately acquiring a shock wave distortion image in a real model experiment.
In order to achieve the purpose, the invention provides the following scheme:
a PIV image calibration device based on laser linear array includes:
the laser emitting component is used for emitting laser linear arrays with equal spacing characteristics to form laser linear array optical paths;
the optical component is used for carrying out light splitting treatment on the laser line in the laser linear array light path so as to form a laser grating in an experimental observation area;
the camera is used for acquiring a distorted laser grating image when the working condition of the wind tunnel experimental section model is adjusted to a PIV experimental working condition; the experimental observation area is positioned above the wind tunnel experimental section model;
and the background processor is used for calibrating and repairing the distorted laser grating image based on a distortion recovery calibration algorithm of the neural network so as to obtain a reconstructed laser grating image.
Optionally, the laser emitting component includes a fixing frame and a plurality of laser pens;
the laser pens are arranged on the fixing frame in a parallel arrangement mode, and the distances between any two adjacent laser pens are equal;
when the laser pen works, all laser lines in the emitted laser linear array are parallel and coplanar by adjusting the installation angle of the laser emitting component and the distance between two adjacent laser pens.
Optionally, the optical component includes a half-reflecting and half-transmitting mirror and a total reflection mirror sequentially arranged on the laser linear array light path;
when the experimental observation area works, the installation angle of the semi-reflecting and semi-transmitting mirror is adjusted, so that after a laser line passes through the semi-reflecting and semi-transmitting mirror, one part of the laser line is transmitted, the other part of the laser line is reflected to form a first reflected laser line, and then the first reflected laser line irradiates the experimental observation area;
adjusting the installation angle of the total reflector to enable the laser lines which are transmitted to pass through the total reflector to be totally reflected to form second reflection laser lines, and then irradiating the second reflection laser lines in the experimental observation area;
the first reflected laser line and the second reflected laser line intersect within the experimental observation area to form an interleaved laser grating.
Optionally, after the high-tide wind tunnel is started, the camera is used for acquiring a distorted laser grating image when the working condition of the wind tunnel experimental section model is adjusted to the PIV experimental working condition;
and before the high-tide wind tunnel is opened, the camera is used for acquiring a laser grating image before distortion.
Optionally, the background processor specifically includes:
the distorted two-dimensional angular point coordinate information extraction module is used for extracting the two-dimensional angular point coordinate information of the laser grating on the distorted laser grating image by adopting an angular point detection algorithm;
the system comprises a pre-distortion two-dimensional corner coordinate information determining module, a pre-distortion two-dimensional corner coordinate information determining module and a pre-distortion two-dimensional corner coordinate information determining module, wherein the pre-distortion two-dimensional corner coordinate information determining module is used for determining the pre-distortion two-dimensional corner coordinate information based on a neural network model and the two-dimensional corner coordinate information of the laser grating on the distorted laser grating image;
and the reconstruction module is used for obtaining a reconstructed laser grating image based on the two-dimensional corner point coordinate information before distortion.
Optionally, the neural network model is a three-layer neural network model; the loss function of the neural network model is a mean square error function; the neural network model comprises two hidden layers, and a ReLU activation layer is added behind each neuron;
the input of the neural network model is two-dimensional corner coordinate information of the laser grating on the distorted laser grating image, and the output of the neural network model is corresponding two-dimensional corner coordinate information before distortion.
A PIV image calibration method based on a laser linear array comprises the following steps:
obtaining a distorted laser grating image when the working condition of the wind tunnel experiment section model is adjusted to a PIV experiment working condition; the laser grating is formed in an experimental observation area after laser lines in the laser linear array light path are subjected to light splitting treatment;
and calibrating and repairing the distorted laser grating image based on a distortion recovery calibration algorithm of the neural network to obtain a reconstructed laser grating image.
Optionally, the method further includes:
building a laser emitting component;
the laser emitting component comprises a fixed frame and a plurality of laser pens, the laser pens are arranged on the fixed frame in a parallel arrangement mode, and the distances between any two adjacent laser pens are equal;
when the laser pen works, all laser lines in the emitted laser linear array are parallel and coplanar by adjusting the installation angle of the laser emitting component and the distance between two adjacent laser pens.
Optionally, the method further includes:
arranging a semi-reflecting and semi-transmitting mirror and a total reflector on a laser linear array light path in sequence;
when the laser observation device works, the installation angle of the semi-reflecting and semi-transmitting mirror is adjusted, so that after a laser line passes through the semi-reflecting and semi-transmitting mirror, one part of the laser line is transmitted, the other part of the laser line is reflected to form a first reflected laser line, and then the first reflected laser line irradiates an experiment observation area;
adjusting the installation angle of the total reflector to enable the laser lines which are transmitted to pass through the total reflector to be totally reflected to form second reflection laser lines, and then irradiating the second reflection laser lines in the experimental observation area;
the first reflected laser line and the second reflected laser line intersect within the experimental observation area to form an interleaved laser grating.
Optionally, the calibration algorithm for distortion recovery based on the neural network is used to calibrate and repair the distorted laser grating image to obtain a reconstructed laser grating image, and specifically includes:
extracting two-dimensional corner coordinate information of the laser grating on the distorted laser grating image by adopting a corner detection algorithm;
determining two-dimensional corner coordinate information before distortion based on the neural network model and two-dimensional corner coordinate information of the laser grating on the distorted laser grating image;
and obtaining a reconstructed laser grating image based on the two-dimensional corner point coordinate information before distortion.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a PIV image calibration device and method based on a laser linear array, which are used for collecting laser gratings to replace the traditional real object target, realizing real model experiment calibration under the condition of shock waves and not interfering the real flow field. On the basis, the distorted laser grating image is calibrated and distorted and restored by adopting a distortion restoration calibration algorithm based on a neural network, so that the purpose of accurately obtaining the shock wave distortion image in a real model experiment is achieved, and the spatial resolution of each image is further obtained.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic structural diagram of a PIV image calibration device based on a laser linear array according to the present invention;
FIG. 2 is a schematic flow chart of a PIV image calibration method based on a laser linear array according to the present invention;
FIG. 3 is a flowchart of an image distortion calibration method based on a laser linear array and a neural network according to the present invention;
FIG. 4 is a schematic diagram of a neural network of the present invention;
FIG. 5 is a laser grating pattern before and after distortion for recording in accordance with the present invention; FIG. 5(a) is a laser raster pattern before distortion; FIG. 5(b) is a distorted laser grating pattern; fig. 5(c) shows the laser grating pattern after distortion correction.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a novel PIV image calibration device without a real object target, which is used for replacing the traditional real object target, realizing real model experiment calibration under the condition of shock waves and not interfering a real flow field. And on the basis, the distorted laser grating image is calibrated and distorted and restored by adopting a neural network algorithm.
The invention also aims to provide a software and hardware system for calibrating the two-dimensional PIV image, which realizes the technical scheme and the system realization for acquiring the high-precision image calibration under the non-contact and non-interference conditions.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example one
The embodiment provides a PIV image calibration device based on a laser linear array, which mainly forms a laser grating as a non-object target in an experimental observation area through the laser linear array and an optical assembly. The device is applied to a high Mach number wind tunnel model PIV experiment, and the schematic diagram of the device is shown in figure 1:
and the laser emitting component 3 is used for emitting laser linear arrays with equal spacing characteristics to form laser linear array optical paths.
And the optical component is used for carrying out light splitting treatment on the laser line in the laser linear array light path so as to form a laser grating in the experimental observation area.
The camera 6 is used for acquiring a distorted laser grating image when the working condition of the wind tunnel experimental section model 1 is adjusted to a PIV experimental working condition; the experimental observation area is positioned above the wind tunnel experimental section model 1.
And the background processor is used for calibrating and repairing the distorted laser grating image based on a neural network algorithm to obtain a reconstructed laser grating image.
As a preferred implementation manner, the laser linear array 3 described in this embodiment includes a fixing frame and a plurality of high-power laser pens installed on the fixing frame.
The plurality of laser pens are arranged on the fixing frame in a parallel arrangement mode, and the distances between any two adjacent laser pens are equal.
When the laser pen works, all laser lines in the emitted laser linear array are parallel and coplanar by adjusting the installation angle of the laser emitting component and the distance between two adjacent laser pens.
Further, this embodiment employs 10 sets of continuous helium-neon laser pens with a power of 1W to produce green light at 633nm wavelength.
As a preferred embodiment, the optical assembly of the present embodiment includes a semi-reflecting and semi-transparent mirror 4 and a total reflection mirror 5 arranged on the optical path of the laser array. The half-reflecting and half-transmitting mirror 4 and the total reflection mirror 5 are both positioned above the wind tunnel experiment section model 1.
When the laser observation device works, the installation angle of the half-reflecting and half-transmitting mirror 4 is adjusted, so that after a laser line passes through the half-reflecting and half-transmitting mirror 4, a part of the laser line is transmitted, the other part of the laser line is reflected to form a first reflected laser line, and then the first reflected laser line irradiates an experimental observation area.
And adjusting the installation angle of the total reflector 5, so that the laser rays transmitted through the total reflector 5 are totally reflected to form second reflected laser rays, and then the second reflected laser rays irradiate in an experimental observation area.
The first and second reflected laser lines intersect within the experimental observation area to form an interleaved laser grating.
Further, the material of the transflective mirror 4 and the total reflection mirror 5 described in this embodiment is a material such as nickel plating.
As a preferred embodiment, in this embodiment, after the laser grating is adjusted, the camera 6 for PIV shooting needs to be arranged; the installation position and the installation angle of the camera 6 are adjusted to ensure that an experimental observation area can be captured.
After the high-tide wind tunnel is opened, shock waves are generated near the surface of the wind tunnel experiment section model, and at the moment, the laser grating image shot again by the camera 6 is the distorted laser grating image. Therefore, the camera 6 at the moment is used for obtaining the distorted laser grating image when the working condition of the wind tunnel experiment section model is adjusted to the PIV experiment working condition.
Before the high-tide wind tunnel is started, the camera 6 is used for acquiring a laser grating image before distortion so as to perform subsequent neural network training.
Further, the camera 6 described in this embodiment is a double-exposure CCD camera. And the camera 6 is controlled by software to record and shoot the laser grating before and after the wind tunnel runs respectively. And the camera data is transmitted to a background processor for storage by adopting a high-speed Cameralink data line.
Further, the wind tunnel described in this embodiment is used to generate uniform and stable high-speed airflow, and the experimental model is pre-arranged in the experimental section, and the tracer particles 2 are scattered in the experimental section, so as to enhance the display effect of the laser grating on the image.
As a preferred embodiment, after recording the laser raster images before and after the distortion, the distorted laser raster image generated by the shock wave can be calibrated and corrected by using the distortion recovery calibration algorithm based on the neural network proposed in this embodiment.
Firstly, the corner detection is respectively carried out on two recorded laser grating images, and corresponding two-dimensional corner coordinate information is extracted. Because the whole space position does not change, the corner point coordinates detected by the front laser grating image and the back laser grating image correspond to each other one by one.
And secondly, constructing a three-layer neural network structure, inputting two-dimensional corner coordinate information extracted from the distorted laser grating image, and outputting the two-dimensional corner coordinate information extracted from the distorted laser grating image. And dividing the extracted two-dimensional corner coordinate information data into a training set and a verification set, and training the neural network structure by adopting a proper training strategy until the fitting precision is reached to obtain a required neural network model. Such a neural network model implies distortion information of the entire image.
And finally, inputting the coordinates of each point on the distorted laser grating image into the neural network model to output the coordinates of the real image after distortion reduction, so as to finish the calibration and distortion repair of the distorted laser grating image.
Compared with the traditional real object target method, the laser grating adopted by the embodiment has no influence on the real flow field, and can record the real distortion image caused by the shock wave.
Example two
Referring to fig. 2, the present embodiment provides a laser-linear-array-based PIV image calibration method, which is applied to the laser-linear-array-based PIV image calibration apparatus in the first embodiment, and the method includes:
step 201: obtaining a distorted laser grating image when the working condition of the wind tunnel experiment section model is adjusted to a PIV experiment working condition; the laser grating is formed in an experimental observation area after laser lines in the laser linear array light path are subjected to light splitting treatment.
Step 202: and calibrating and repairing the distorted laser grating image based on a distortion recovery calibration algorithm of the neural network to obtain a reconstructed laser grating image.
Further, the method for calibrating a PIV image based on a laser line array according to this embodiment further includes:
and building a laser emitting component.
The laser emitting component comprises a fixed frame and a plurality of laser pens, the laser pens are arranged on the fixed frame in a parallel arrangement mode, and the distances between any two adjacent laser pens are equal; when the laser pen works, all laser lines in the emitted laser linear array are parallel and coplanar by adjusting the installation angle of the laser emitting component and the distance between two adjacent laser pens.
Further, the method for calibrating a PIV image based on a laser line array according to this embodiment further includes:
and a semi-reflecting and semi-transparent mirror and a total reflector are sequentially arranged on the laser linear array light path.
When the laser observation device works, the installation angle of the semi-reflecting and semi-transmitting mirror is adjusted, so that after a laser line passes through the semi-reflecting and semi-transmitting mirror, one part of the laser line is transmitted, the other part of the laser line is reflected to form a first reflected laser line, and then the first reflected laser line irradiates an experiment observation area; adjusting the installation angle of the total reflector to enable the laser lines which are transmitted to pass through the total reflector to be totally reflected to form second reflection laser lines, and then irradiating the second reflection laser lines in the experimental observation area; the first reflected laser line and the second reflected laser line intersect within the experimental observation area to form an interleaved laser grating.
Further, step 202 specifically includes:
and extracting the two-dimensional corner coordinate information of the laser grating on the distorted laser grating image by adopting a corner detection algorithm.
And determining two-dimensional corner coordinate information before distortion based on the neural network model and the two-dimensional corner coordinate information of the laser grating on the distorted laser grating image.
And obtaining a reconstructed laser grating image based on the two-dimensional corner point coordinate information before distortion.
EXAMPLE III
The present embodiment provides an image distortion calibration method based on a laser array and a neural network, please refer to fig. 3, which includes:
step 1: building a laser linear array light path; the method specifically comprises the following steps:
and a plurality of laser pens are arranged on the fixing frame, and the installation distance and the installation angle of the laser pens are adjusted to enable the laser pens to emit coplanar and parallel laser linear arrays and form laser linear array light paths.
Step 2: adjusting the optical lens to form a grating; the method specifically comprises the following steps:
step 2.1: firstly, arranging a semi-reflecting and semi-transmitting mirror on a laser linear array light path; the semi-reflecting and semi-transmitting mirror is positioned above the wind tunnel experiment section model and used for directly transmitting and reflecting a part of laser lines of the laser linear array; and then adjusting the mounting position and the mounting angle of the half-reflecting and half-transmitting mirror to enable the reflected light to illuminate an experimental observation area, namely a flowing observation area.
Step 2.2: firstly, arranging a total reflection mirror on a light path of a transmission light ray; the total reflector is positioned above the wind tunnel experimental section model and used for totally reflecting the transmitted light; and secondly, adjusting the mounting position and the mounting angle of the total reflector to ensure that the reflected transmitted light also illuminates an experimental observation area, and then intersecting the reflected light passing through the semi-reflecting and semi-transmitting mirror to form a laser grating.
And step 3: collecting images before and after distortion; the method specifically comprises the following steps:
step 3.1: firstly, erecting a camera on an experiment bench; and then adjusting the installation position and the installation angle of the camera to enable the camera to accurately capture the experimental observation area.
Step 3.2: tracer particles are scattered in the wind tunnel experiment section to enhance the reflection effect of the laser grating.
Step 3.3: before the wind tunnel is opened, a camera is used for recording a laser grating image, and the laser grating on the laser grating image is not distorted.
Step 3.4: starting a high-tide wind tunnel, adjusting the working condition of a wind tunnel experiment section to the PIV experiment working condition, generating shock waves on the surface of a model of the wind tunnel experiment section at the moment, twisting the laser grating, and finally recording a distorted laser grating image by using a camera;
and 4, step 4: detecting an angular point; the method specifically comprises the following steps:
and respectively extracting two-dimensional corner coordinate information of the laser grating on the laser grating image before distortion and the laser grating image after distortion by adopting a corner detection algorithm.
The corner detection algorithm is as follows:
moving a window with a set size in each direction of the laser grating image, and calculating an autocorrelation function of gray level change in the window in the moving process, as shown in formula (1):
E(u,v)＝∑x,yw(x,y)[I(x+u,y+v)-I(x,y)]2 (1)；
wherein, (u, v) is the size of the window; w is the weight of the window and is taken as 1; i is the image pixel gray value; (x, y) are pixel coordinates.
The autocorrelation function E after taylor expansion can be written as:
the formula for M is:
defining the corner point corresponding function R as:
R＝detM-k(traceM)2 (4)；
traceM＝λ1+λ2 (5)；
detM＝λ1λ2 (6)；
wherein traceM is a trace of the matrix M; detM is the rank of the matrix M; lambda [ alpha ]1And λ2Is the eigenvalue of the matrix M; k is an empirical constant, and is generally 0.04-0.06.
And when the R is detected to be larger than 0, the position of the angular point can be positioned and the two-dimensional angular point coordinate information can be extracted.
And 5: and constructing a neural network.
Referring to fig. 4, the neural network includes two hidden layers, and a ReLU activation layer is added after each neuron. The computational mathematical expression of the neuron is as follows:
and calculating the loss of the neural network by adopting a mean square error function, namely the loss function of the neural network is as follows:
wherein, (x, y) is a predicted coordinate output by the neural network, and (x ', y') is a real coordinate output by the neural network, namely a two-dimensional corner coordinate before distortion determined by a corner detection algorithm. n is the number of batchs of a batch in the training process.
Step 6: training to obtain a neural network model; the input of the neural network model is two-dimensional angular point coordinate information after distortion, and the output is two-dimensional angular point coordinate information before distortion.
And combining the two-dimensional corner coordinate information before distortion and the two-dimensional corner coordinate information after distortion which are detected before the distortion into a training set sample, and taking 8 samples as a group to be used as a batch to train the weight of the neural network.
Wherein, the Adam optimization learning algorithm is selected for neural network optimization training. The optimization process is as follows:
step 6.1: weights in initializing neural networks are noted as θ0Initializing a first moment of momentum m0Second moment of momentum v0Learning rate α is 0.00001 and parameter weight β1＝0.9、β2＝0.999、ε＝10-8。
Step 6.2: under the current weight, a batch of samples are brought into to calculate the Loss of the neural networkt(θt-1) And solving the gradient of the weight theta, wherein the calculation formula is as follows:
wherein t represents the current iteration number, and t-1 is the last iteration number.
Step 6, 3: calculating the moment of first order momentum with deviation and the moment of second order momentum with deviation, wherein the calculation formula is as follows:
mt＝β1×mt-1+(1-β1)gt (10)；
vt＝β2×vt-1+(1-β2)gt 2 (11)；
step 6.4: calculating an unbiased first-order moment of momentum and an unbiased second-order moment of momentum by the following calculation formula:
step 6.5: calculating and updating the weight of the neural network, wherein the calculation formula is as follows:
step 6.6: and (6.2) repeating the steps 6.5 until the loss is not reduced any more, and considering that the training is finished.
Step 6.7: and verifying the prediction accuracy of the neural network model by using the unused two-dimensional corner coordinate information as a verification set, and determining that the neural network model meets the requirements when the accuracy is higher than 90%.
And 7: and finishing calibration and repairing image distortion.
After a neural network model containing distortion information is obtained, extracting each pixel point (x, y, I) on the distorted laser grating image; wherein I is the gray scale information on the pixel. After the coordinates (x, y) are input into the neural network model containing the distortion information, the coordinates (x ', y') on the laser raster image before distortion are obtained through prediction, and all pixel points (x, y, I) on the laser raster image after distortion are traversed, so that the corresponding laser raster image before distortion can be reconstructed, and the effect of the laser raster image before distortion is shown in fig. 5.
The invention discloses a PIV image calibration device and method based on a laser linear array, which comprises the following steps: the laser emitting component emits a series of laser linear arrays with equal spacing, a plurality of groups of optical lenses are arranged on the light path of the laser linear arrays to reflect and project laser lines, namely, the light splitting of the laser linear arrays is realized, and laser grids which are vertically crossed with the laser linear arrays are formed near the wind tunnel experimental section model by reasonably arranging the installation positions and the installation angles of the optical lenses. And arranging a camera outside an observation window of the wind tunnel experimental section model, and capturing a high-definition image of the laser grid by using the camera.
When the wind tunnel runs, under the action of high-speed airflow, shock waves are generated near an experimental observation area of the wind tunnel experimental section model, and the projection of local laser grating grids on an image generates distortion due to the generation of the shock waves so as to form a distorted image.
Recording high-definition images of two frames of laser grids before and after the operation of the wind tunnel, respectively detecting the two recorded images before and after the operation of the wind tunnel by adopting an angular point detection algorithm, extracting coordinates of intersection points of all the identified laser grid grids, constructing a neural network model based on the identified coordinates, performing model training by taking distorted angular point coordinates as input and corresponding undistorted angular point coordinates as output true values, and thus constructing the neural network model. And inputting the distorted image acquired by the camera into the neural network model to finish the calibration of the PIV image.
The device and the method provide a calibration solution without placing target objects, solve the problem of image distortion caused by shock waves near a model in the process of PIV measurement in a high-tide wind tunnel, and improve the accuracy of distortion correction by adopting a neural network model to fit distortion.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (10)
1. A PIV image calibration device based on laser linear array is characterized by comprising:
the laser emitting component is used for emitting laser linear arrays with equal spacing characteristics to form laser linear array optical paths;
the optical component is used for carrying out light splitting treatment on the laser line in the laser linear array light path so as to form a laser grating in an experimental observation area;
the camera is used for acquiring a distorted laser grating image when the working condition of the wind tunnel experimental section model is adjusted to a PIV experimental working condition; the experimental observation area is positioned above the wind tunnel experimental section model;
and the background processor is used for calibrating and repairing the distorted laser grating image based on a distortion recovery calibration algorithm of the neural network so as to obtain a reconstructed laser grating image.
2. The PIV image calibration device based on the laser linear array as recited in claim 1, wherein the laser emitting component comprises a fixed frame and a plurality of laser pens;
the laser pens are arranged on the fixing frame in a parallel arrangement mode, and the distances between any two adjacent laser pens are equal;
when the laser pen works, all laser lines in the emitted laser linear array are parallel and coplanar by adjusting the installation angle of the laser emitting component and the distance between two adjacent laser pens.
3. The PIV image calibration device based on the laser array as recited in claim 1, wherein the optical assembly comprises a semi-reflecting and semi-transparent mirror and a total reflection mirror which are sequentially arranged on the light path of the laser array;
when the experimental observation area works, the installation angle of the semi-reflecting and semi-transmitting mirror is adjusted, so that after a laser line passes through the semi-reflecting and semi-transmitting mirror, one part of the laser line is transmitted, the other part of the laser line is reflected to form a first reflected laser line, and then the first reflected laser line irradiates the experimental observation area;
adjusting the installation angle of the total reflector to enable the laser lines which are transmitted to pass through the total reflector to be totally reflected to form second reflection laser lines, and then irradiating the second reflection laser lines in the experimental observation area;
the first reflected laser line and the second reflected laser line intersect within the experimental observation area to form an interleaved laser grating.
4. The PIV image calibration device based on the laser linear array as recited in claim 1,
after the high-tide wind tunnel is started, the camera is used for obtaining a distorted laser grating image when the working condition of the wind tunnel experiment section model is adjusted to the PIV experiment working condition;
and before the high-tide wind tunnel is opened, the camera is used for acquiring a laser grating image before distortion.
5. The PIV image calibration device based on the laser linear array as claimed in claim 1, wherein the background processor specifically comprises:
the distorted two-dimensional angular point coordinate information extraction module is used for extracting the two-dimensional angular point coordinate information of the laser grating on the distorted laser grating image by adopting an angular point detection algorithm;
the system comprises a pre-distortion two-dimensional corner coordinate information determining module, a pre-distortion two-dimensional corner coordinate information determining module and a pre-distortion two-dimensional corner coordinate information determining module, wherein the pre-distortion two-dimensional corner coordinate information determining module is used for determining the pre-distortion two-dimensional corner coordinate information based on a neural network model and the two-dimensional corner coordinate information of the laser grating on the distorted laser grating image;
and the reconstruction module is used for obtaining a reconstructed laser grating image based on the two-dimensional corner point coordinate information before distortion.
6. The PIV image calibration device based on the laser linear array as recited in claim 5, wherein the neural network model is a three-layer neural network model; the loss function of the neural network model is a mean square error function; the neural network model comprises two hidden layers, and a ReLU activation layer is added behind each neuron;
the input of the neural network model is two-dimensional corner coordinate information of the laser grating on the distorted laser grating image, and the output of the neural network model is corresponding two-dimensional corner coordinate information before distortion.
7. The calibration method applied to the laser-array-based PIV image calibration device of claim 1 is characterized by comprising the following steps:
obtaining a distorted laser grating image when the working condition of the wind tunnel experiment section model is adjusted to a PIV experiment working condition; the laser grating is formed in an experimental observation area after laser lines in the laser linear array light path are subjected to light splitting treatment;
and calibrating and repairing the distorted laser grating image based on a distortion recovery calibration algorithm of the neural network to obtain a reconstructed laser grating image.
8. The calibration method according to claim 7, further comprising:
building a laser emitting component;
the laser emitting component comprises a fixed frame and a plurality of laser pens, the laser pens are arranged on the fixed frame in a parallel arrangement mode, and the distances between any two adjacent laser pens are equal;
when the laser pen works, all laser lines in the emitted laser linear array are parallel and coplanar by adjusting the installation angle of the laser emitting component and the distance between two adjacent laser pens.
9. The calibration method according to claim 7, further comprising:
arranging a semi-reflecting and semi-transmitting mirror and a total reflector on a laser linear array light path in sequence;
when the laser observation device works, the installation angle of the semi-reflecting and semi-transmitting mirror is adjusted, so that after a laser line passes through the semi-reflecting and semi-transmitting mirror, one part of the laser line is transmitted, the other part of the laser line is reflected to form a first reflected laser line, and then the first reflected laser line irradiates an experiment observation area;
adjusting the installation angle of the total reflector to enable the laser lines which are transmitted to pass through the total reflector to be totally reflected to form second reflection laser lines, and then irradiating the second reflection laser lines in the experimental observation area;
the first reflected laser line and the second reflected laser line intersect within the experimental observation area to form an interleaved laser grating.
10. The calibration method according to claim 7, wherein the calibration algorithm for the distortion recovery based on the neural network calibrates and repairs the distorted laser grating image to obtain the reconstructed laser grating image, specifically comprising:
extracting two-dimensional corner coordinate information of the laser grating on the distorted laser grating image by adopting a corner detection algorithm;
determining two-dimensional corner coordinate information before distortion based on the neural network model and two-dimensional corner coordinate information of the laser grating on the distorted laser grating image;
and obtaining a reconstructed laser grating image based on the two-dimensional corner point coordinate information before distortion.
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